This invention relates to a novel binder system for agglomerates. This invention also relates to a novel binder system for agglomerates suitable for use in a direct arc furnace for production of silicon or ferrosilicon metal. The binder system of this invention produces agglomerates which can withstand the environment of a direct arc furnace better than prior art agglomerates.
Agglomerates have been used in the production of metals and metal alloys, including silicon and silicon-containing alloys, by the carbothermic reduction of the corresponding metal oxides. For example, Schei et al. in U.S. Pat. No. 3,218,153 (issued Nov. 16, 1965) prepare silicon and other metals from pellets or briquetts consisting of a core which contains an excess of the metal oxide surrounded by a second layer or shell which contains an excess of the carbonaceous reducing agent. Schei et al. employed conventional binders such as Portland or alumina cement, molasses, bentonite or sulphite lye to prepare the agglomerates.
Ilinkov et al. in U.S. Pat. No. 3,892,558 (issued Jul. 1, 1975) prepared aluminum-silicon alloys using briquettes in an electric arc furnace. The briquettes were prepared using an alcohol-sulphite lye binder.
Das et al. in U.S. Pat. No. 4,046,558 (issued Sept. 6, 1977) prepared aluminum-silicon alloys from briquettes containing metal oxides and a carbonaceous reducing agent in a blast or electric arc furnace. The briquettes did not contain any additional binder.
Ryabchikov et al. in U.S. Pat. No. 4,155,753 (issued May 22, 1979) disclosed a continuous one step process for the production of silicon-containing ferro alloys employing briquettes in a smelting furnace. The briquettes did not contain any additional binder.
Furui et al. in U.S. Pat. No. 4,168,966 (issued Sept. 25, 1979) employed pellets and briquettes containing iron ores in a blast furnace. The pellets or briquettes contained iron ore, additives, and a hydraulic binder. Hydraulic binders included portland cement, portland cement clinker, alumina cement, alumina cement clinker, cement mixed with blast furnace slag, cement mixed with fly ash, cement mixed with borazon and masonry-mixed cement.
Merkert in U.S. Pat. Nos. 4,309,216 (issued Jan. 5, 1982) and 4,395,285 (issued Jul. 26, 1983) prepared low density, porous compacts containing silica fume, finely-divided carbonaceous reducing agents such as petroleum coke or coal and, optionally, iron and a binder, in preparing silicon and ferrosilicon. The binder was a cereal binder such as corn starch.
Lask in U.S. Pat. Nos. 4,366,137 (issued Dec. 28, 1982) and 4,389,493 (issued June 21, 1983) prepared silicon in an electric furnace using briquettes containing quartz and a caking coal. The briquettes were prepared by hot briquetting the formed body at 350.degree.-550.degree. C. No additional binders were used.
Kuwahara in U.S. Pat. No. 4,394,167 (issued Jul. 19, 1983) disclosed a process of carbothermically producing aluminum using briquettes prepared from alumina, silica, and iron oxide bearing materials and coking coal. The briquettes were formed by heating the formed mixture to 600.degree.-900.degree. C. The direct coking operation is said to eliminate the volatile matter in the coal and produce an alumina bearing coked briquette which has a porous coked structure. No additions binders are employed in the process of Kuwahara.
Sodium and calcium lignosulfonates have been used as binders for preparing briquettes of silicon and ferrosilicon dust by Aitcin et al. in U.S. Pat. No. 4,348,230 (issued Sept. 7, 1982). Such briquettes do not contain either metal oxides or reducing agents.
The agglomerates found in the prior art generally lack the physical strength to function well in the demanding environment of a blast, smelting, or electric arc furnace over the entire temperature range found in such environments. The prior art agglomerates generally lack sufficient strength at either low or high temperatures. The prior art agglomerates which possess sufficient strength at high temperatures generally do not possess sufficient strength at low temperatures. And the prior art agglomerates which possess sufficient strength at low temperatures generally do not possess sufficient strength at high temperatures. Agglomerates which have sufficient strength at both low and high temperatures would be very desirable.
It is an object of this invention to provide agglomerates which have sufficient strength at both low and high temperatures. It is another object of this invention to provide agglomerates which have adequate strength to survive the environment of a blast, smelting or electric arc furnace over a wide temperature range. It is still another object of this invention to provide agglomerates containing metal oxide-containing materials, carbonaeous reducing agents, and a mixed binder system. It is still another object of this invention to provide a method of preparing metals and metal alloys, especially silicon and silicon-containing alloys, using agglomerates prepared using a mixed binder system. Other objects will be apparent upon a consideration of this specification.